EVOLUTIONARY. PROBLEM SOLVING. Thomas Philip Runarsson. Faculty of Engineering. Reykjavik 2000 ... The work presented is a study of a problem solving technique inspired by the principles of biological evolution. Solving a problem is ..... 101] in which both are acting as both, the problem and solution. By isolating ...
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EVOLUTIONARY PROBLEM SOLVING
Thomas Philip Runarsson
Faculty of Engineering Reykjavik 2000
Copyright 2000 Thomas Philip Runarsson All Rights Reserved ISBN 9979-9494-1-4 H´ask´ ola´ utg´ afan University of Iceland
This thesis has been accepted by the Faculty of Engineering of the University of Iceland for public defence in fulfilment of the requirements for the degree of doctor scientiarum ingeniarius.
Faculty of Engineering Reykjavik, 29th January 2001 Valdimar K. Jonsson, Dean
Thesis Committee:
Professor Magnus Thor Jonsson Professor Xin Yao Professor Hans-Paul Schwefel
Preface This thesis on evolutionary problem solving is a summation of work accomplished over a period of four years. My interest in this field was aroused when unintentionally attending an IEEE workshop on genetic algorithms in 1994. There are numerous people to thank for making this work possible: First of all Magnus Thor Jonsson for his encouragement, and creating the liberty to pursue this area of research. Xin Yao for sharing his expertise and guidance. Einar Arnason for endless discussions on evolutionary processes and natural systems. John Stuart for his patience in discussing the nature of representations. Gudmundur R. Jonsson for helping with difficult statistics. J¨orgen Pind for renewing my interest in connectionist models. Mikael Karlson for making me doubt everything. Ruhul Sarker for generating interest in constrained problems. Hans-Paul Schwefel and David B. Fogel for sharing their insight into the working principles of evolutionary computation. Hans-George Beyer for discussions on theories for evolution strategies. Richard Sutton for pointing out the problems with evolutionary computation. Finally, I thank the Department of Mechanical Engineering and my many friends there for creating an invigorating academic environment. Financial support for this work was provided by the Research Council of Iceland and the Research Fund of the University of Iceland. Travel grants were awarded by the Engineering Labour Union and the University of Iceland. Many thanks to the Department of Computer Science at the Australian Defence Force Academy for hosting me in Canberra, in particular Bob McKay and Charles Newton. Thomas Philip Runarsson Faculty of Engineering, University of Iceland Reykjavik, December 2000.
Abstract The work presented is a study of a problem solving technique inspired by the principles of biological evolution. Solving a problem is the transformation of a given situation into a desired one. The work may be divided into three main interdependent areas of research: (1) describing a situation, (2) operator design for changing a situation, and (3) evaluation by selection. Evolutionary problem solvers are inspired from a model of natural evolutionary processes where organisms are ‘solutions’ to ‘problems’ set up by the environment. Therefore, how an organism and its environment are represented on a computational device is of central interest in the work. Experimental studies and examples are given illustrating the use of symbolic and connectionist representations in evolutionary problem solving. The plausibility that the syntactical manipulation of symbols is an effective and efficient approach to evolutionary search is questioned. For ‘intelligent’ search operators must essentially infer the location of better solutions and for this the symbols must be transformed based on their meaning. It is often difficult to interpret how evolutionary search methods locate good solutions. If a landscape is described by the parent position and the expected fitness of the best offspring, then its topology will determine when evolutionary search locates on average the desired goal. An interpretation of this landscape assists in the design of variation operators and in determining the number of offspring required. The analysis is also useful for the understanding of a new rank-based selection method presented for the treatment of infeasible solutions.